1. Field of the Invention
This invention relates to an apparatus for practising temperature gradient zone melting and more specifically an apparatus for an automated practice of temperature gradient zone melting.
2. Description of the Prior Art
In the manufacture of semiconductor devices, it is often necessary to alter or tailor the conductivity type of a body of semiconductor material. This alteration is achieved by distributing atoms of a conductivity modifying dopant in a selected region or selected regions of the body. Frequently, techniques employed to achieve that distribution require the heating of the semiconductor body.
Recently, it has been discovered that a preferred technique of altering the conductivity of a semiconductor body is the technique of temperature gradient zone melting. Early teachings of temperature gradient zone melting are found in U.S. Pat. No. 2,813,048 issued to W. G. Pfann and in a book by Pfann entitled Zone Melting (John Wiley and Sons, Inc., 1966). More recent applications of temperature gradient zone melting are disclosed and claimed in U.S. Pat. Nos. 3,899,361 and 3,899,362 to Thomas R. Anthony and Harvey E. Cline and assigned to the same assignee of the present invention. The aforementioned patents to Anthony and Cline are incorporated herein by reference. As taught in the aforementioned book by Pfann, temperature gradient zone melting involves the migration of a melt of a first material through a body of a second material under the influence of a temperature gradient maintained across the second material and finally a recrystallization of the melt after migration. In the application of temperature gradient zone melting to the production of semiconductor devices, the first material usually comprises a metal such as aluminum, tin-aluminum alloy or gold-antimony alloy while the second material comprises a semiconductor material such as silicon, germanium or the like.
In his copending U.S. Pat. application Ser. No. 578,736, filed May 19, 1975, U.S. Pat. No. 4,041,278, and entitled "Heating Apparatus For Temperature Gradient Zone Melting" John Boah discloses a furnace suitable for the manufacture of semiconductor devices by temperature gradient zone melting. However, it was found that the Boah apparatus could be improved upon in a number of respects. A new and improved heater useful in such a furnace is disclosed and claimed in the aforementioned U.S. Pat. No. 4,101,759 incorporated herein by reference. This heater provides a heat output capability commensurate with a large scale commercial manufacture of semiconductor devices, the temperature gradient across an array of semiconductor devices heated by this heater being of a uniformity sufficient to ensure consistency in the simultaneous production of a plurality of semiconductor devices.
Another furnace suitable for processing semiconductor bodies by temperature gradient zone melting is disclosed and claimed in U.S. Pat. No. 4,097,226 previously cited and incorporated herein by reference. This furnace is particularly well suited for a large scale manufacture of semiconductor devices by temperature gradient zone melting due to its simplicity of construction, potential for accommodating a large number of semiconductor bodies simultaneously and the accessibility of the work chamber or interior of the furnace by automated loading and unloading apparatus.
Large scale commercial manufacture of semiconductor devices necessarily requires automated apparatus for the transfer of semiconductor bodies from one work station to a successive station. Therefore, such a commercial manufacture of semiconductor devices by temperature gradient zone melting, requires automated apparatus for the loading of semiconductor wafers from the furnace. To optimize the processing, such a loading and unloading should be accomplished as rapidly and simply as possible.
The semiconductor wafers, before being loaded into the furnace, have undergone considerable processing which may include, among others, the processing steps of selective coating, metallization, impurity introduction, selective removal of surface materials and cleaning, each process adding to the value of the wafers. The wafers are generally quite brittle and of a typical thickness of only 6 to 12 mils making the wafers quite fragile. Therefore, any apparatus for the automated loading of wafers into a furnace and unloading from a furnace must carry out these functions without damaging the valuable yet fragile wafers.
Accordingly, it is an object of the present invention to provide an apparatus for practising temperature gradient zone melting which overcomes the deficiencies of the prior art.
It is another object of the present invention to provide an apparatus for the practise of temperature gradient zone melting wherein semiconductor wafers are loaded into and unloaded from a furnace in a simple manner requiring a minimal amount of time.
It is another object of the present invention to provide an apparatus for the practise of temperature gradient zone melting wherein semiconductor wafers are loaded into and unloaded from a furnace with only minimal risk of damaging the wafers.